Merge #13579: teach string.Formatter about 'a'.

Patch by Francisco Martín Brugué.

2 files changed, 12 insertions, 4 deletions

diff --git a/Lib/string.py b/Lib/string.py
index 8bcd1dc..b57c79b 100644
--- a/Lib/string.py
+++ b/Lib/string.py
@@ -220,12 +220,14 @@ class Formatter:
 
     def convert_field(self, value, conversion):
         # do any conversion on the resulting object
-        if conversion == 'r':
-            return repr(value)
+        if conversion is None:
+            return value
         elif conversion == 's':
             return str(value)
-        elif conversion is None:
-            return value
+        elif conversion == 'r':
+            return repr(value)
+        elif conversion == 'a':
+            return ascii(value)
         raise ValueError("Unknown conversion specifier {0!s}".format(conversion))
 
 
diff --git a/Lib/test/test_string.py b/Lib/test/test_string.py
index 1615732..c2bdfdb 100644
--- a/Lib/test/test_string.py
+++ b/Lib/test/test_string.py
@@ -37,6 +37,12 @@ class ModuleTest(unittest.TestCase):
         self.assertEqual(fmt.format("-{arg!r}-", arg='test'), "-'test'-")
         self.assertEqual(fmt.format("{0!s}", 'test'), 'test')
         self.assertRaises(ValueError, fmt.format, "{0!h}", 'test')
+        # issue13579
+        self.assertEqual(fmt.format("{0!a}", 42), '42')
+        self.assertEqual(fmt.format("{0!a}",  string.ascii_letters),
+            "'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'")
+        self.assertEqual(fmt.format("{0!a}",  chr(255)), "'\\xff'")
+        self.assertEqual(fmt.format("{0!a}",  chr(256)), "'\\u0100'")
 
     def test_name_lookup(self):
         fmt = string.Formatter()